The present invention relates generally to turbines and compressors, and, more specifically, to an improved mechanism for damping vibrations and sealing the spaces between the adjacent platform portions of a row of circumferentially spaced blades in a gas turbine engine.
Gas turbine engines typically have a plurality of rows of circumferentially spaced rotor blades mounted on a disk for rotation therewith about the disk axis. These blades exist in a myriad of different shapes and configurations, but generally have an innermost root portion, an intermediate platform portion and an outermost airfoil portion. The root portion, also known as a dovetail, commonly has an inverted "fir tree"-like shape or appearance, and is slidably received in a complimentarily configured recess provided in the rotor disk. The platform portions separate the root and airfoil portions of the blades, and collectively define an outwardly facing wall of an annular gas flow passageway through the engine. The airfoil portions typically extend radially into the passageway to interact with the gas flow therethrough. At the same time, however, these airfoil portions constitute cantilevered members which are subject to fatigue due to vibrations. This problem is particularly acute since the disk may be rotated at angular speeds ranging from zero to 45,000 r.p.m. and beyond.
The source and nature of such blade vibrations are difficult to understand, identify and eliminate. Such vibrations may, in fact, be functions of many variables, some controllable and others not. In any event, there is a general need and desire to damp such vibrations to reduce the fatigue on the blades, particularly at or near resonant frequencies. At the same time, there is also a need to effectively seal the space between the platform portions of adjacent blades to confine the gas flow to the annular passageway.
Various types of blade dampers are known. For example, in a shroud-type damper, the distal ends of adjacent airfoil portions are physically connected to one another. While this design places a blade-to-blade connecting member at the greatest radial distance from the rotor disk axis, and may indeed constitute an effective damper, it increases the mass of the airfoil portions, does not contribute to sealing of the space between adjacent platform portions, and may interfere with the gas flow through the passageway.
Under-platform dampers are also known. These devices generally have a movable member operatively positioned between the rotor disk and the underside of the platform portion(s) of one or more blades. Upon rotation of the turbine, this member is adapted to be centrifugally forced radially outwardly into fluid-tight sealed engagement with the underside surfaces of adjacent blades. While these arrangements may provide an effective seal between the adjacent platform portions, and may provide an effective vibration damper in some applications, the points of contact between the member and the blade(s) are typically located on the underside of the platform portions.